This application is directed to a continuous bulk polymerization processes and associated apparatuses for preparing polymeric compositions using a recirculation tubular loop reactor system and, more particularly, a continuous bulk polymerization process that utilizes plug flow and associated apparatuses for preparing polymeric compositions, such as adhesives, using a recirculation tubular loop reactor including a planetary roller extruder (PRE) and/or static mixers.
Conventional bulk polymerization processes for producing adhesives by polymerization are known in the art. One such process includes a stirred tank reactor having a cooling jacket for removing heat from the vessel generated during the exothermic reaction therein. Such conventional processes have been somewhat effective at low conversion rates. However, at high conversion rates and associated high viscosities, the heat transfer surfaces often foul, thereby losing temperature control and facilitating runaway reactions. Mandating low conversion rates has not presented an economical solution to the problem since the excessive monomer used in low conversion operations must eventually be removed from the polymer by, for example, drying, de-volatilization or the like, thereby adding an additional processing step and associated costs. Conversions less than 95% require de-volatilization to remove the excess monomer from the polymer.
It has been found that PREs are well suited to the processing of highly exothermic reactions, such as the free radical polymerization of alkyl acrylate compounds, because thin layers of compound can be exposed to large surface areas thereby resulting in effective heat exchange, mixing and temperature control.
U.S. Published Application 2005/0170086A1 discloses a PRE which is reproduced in FIG. 1 herein. FIG. 1 shows a longitudinal section view of one example of a PRE 10′ including a feeding section 12′ and a compounding section 14′. The primary adhesive raw materials are added into the feed throat 16′ and metered onto the conveying screw 18′ of the feeding section 12′. As used herein, the term “primary raw materials” refers to those materials of the adhesive formulation added into the feed section 12′ of the PRE 10′. Primary raw materials may include, but are not limited to elastomers, resins, extenders, activators, anti-degradents and crosslinking agents. The screw 18′ conveys the primary raw materials into the compounding section 14′. FIG. 1 includes four planetary roller barrel sections 20′a, 20′b, 20′c and 20′d separated by dosing rings 22′a, 22′b and 22′c. Each roller barrel section 20′ includes a 45° helical toothed cylinder 24′, a 45° helical toothed main spindle 26′ and a plurality of 45° helical toothed planetary spindles 28′, 30′. The planetary spindles 28′, 30′ also mesh with the internal gearing of the cylinder section 24′. The helical gearing of the main spindle 26′, the planetary spindles 28′, 30′ and the cylinder section 24′ conveys the raw materials to be compounded in the direction of the discharge orifice 34′. Secondary solid raw materials can be added to the compounding section 14′ through a side feeder 36′ or twin screw dosing units 38′. The twin screw dosing units 38′ are typically positioned perpendicular to the longitudinal axis of the compounding section 14′ and are typically located near the beginning of the compounding section 14′ directly adjacent to the dosing ring 22′a. The twin screw dosing units 38′ can be employed to introduce solid components such as thermoplastic elastomers, resins, extenders, activators, anti-degradents, crosslinkers, etc., to the individual roller barrel sections 20′.
U.S. Pat. No. 4,324,868 teaches that a plug flow type reaction vessels like those proposed in U.S. Pat. No. 3,821,330 and JP Patent Publication No. 4193/73 are not suitable for practicing the disclosed process for the preparation of vinyl polymers by bulk or solution polymerization. The disclosed process includes recycling a portion of the polymer-containing liquid (polymerization mixture) withdrawn from the polymerization zone and returning it to the starting mixture. The process continuously introduces a polymerization starting material containing at least one vinyl monomer, preferably a methyl methacrylate, a polymerization initiator and a polymerization regulator into the polymerization zone and agitating and substantially homogeneously mixing the mixture in the polymerization zone at a temperature of 100-200° C. to effect polymerization so that the polymer content in the resulting reaction mixture is 50%-80% by weight. Likewise, U.S. Pat. No. 3,968,059 teaches that a plug flow type polymerization reactor is not preferable for use with the disclosed bulk polymerization process for polymerizing methyl methacrylate.